Narrow band long range color television system incorporating color analyzer



K. H. GEBEL 3,330,904

R. NARROW BAND LONG RANGE COLOR TELEVISION SYSTEM INCORPORATING COLOR ANALYZER 13 Sheets-Sham 1.

July 1.1, 1967 Filed March 29, 1965 Y sen/son Z SENSO/f INVENTOR A. M 66362 W4? QM BY gm #um July 11, 1967 R. K. H. GEBEL NARROW BAND LONG RANGE coLoR TELEvIsoN SYSTEM INCORPOHATING COLOR ANALYZER Filed March 29, 1965 13 Sheets-Sheet R. K. H. GEBEL NARROW BAND LONG RANGE- COLOR TBLE'JlsION SISTEM INCORPORATINC QOLOR ANALHEN July 11, 1967 l 3 Sheet-s-She f. i 3

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NARROW BAND LIONG RANGE COLOR TELEVISION SYSTEM INCORPORATING COLOR ANALYZER foo 50o v 60G 'loo wnvece'wsrf/ A [my] E L g5 9 mvo ro senso# v Eig-Q INVENTOR 4RM M 6F55( vJuly 11, 1961 Filed March 29, 1965 R. K. H. GEBEL 3,330,904 NARROW BAND LONG RANGE COLOR TELEVISION SYSTEM INCORPORATING COLOR ANALYZER 13 Sheets-Shen 5 50c l 60o 700 wal/Lavera n [m] Eig-7 INVENTOR G'Z HMM July 11, 1967 R. K. H. GEBEL mmaow BAND Lone RANGE coLoR TELEVISION svs'rau INconPoaA'rme conos Muizen 13 Sheets-Sheet 6 Filed llarch 29. 1965 wavcuwcrav l [mln] n m n x d o dtmvAw/ v Arnim wfmd July 1l, 1967 n K H Gase.. 3,330,904

NARROW BAND I ONGl RNGE COLOR TELEVISION SYSTEM INCORPORATING COLOR ANALYZER Filed March 29. 1965 13 Sheets-Sheet 7 l [Trf -l-a TTS-11 *T39-gm n35/WW July 11, 1967 Filed March 29, 1965 R. K. H. GEBEL NARROW BAND LONG RANGE COLOR TELEVISION SYSTEM INCORFORATING COLOR ANALY'IER 13 Sheets-Sheet 8 E'g-EA NVENTOR l?. K. 6666( wy? @MX July 11, 1967 R K. H.csEBE1. 3,330,904

NARROW BAND LONG RANGE COLOR TELEVISION SYSTEM INCORPORATING COLOR ANALYZER Filed March 29, 1965 13 Sheets-Sheet i i wry/re V49 Z ULll :E :L E INVENTOR wfm July l1, 1967 R. K. H. GEBEL. 3,330,904

NARROW BAND LONG RANGE COLOR TELEVISION SYSTEM INCORPORATING COLOR ANALYZER Filed March 29, 1965 13 Sheets-Sheet l0 S- 4 PNoroc/moor 'komm wlarrew 'lcrtk No. I3

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Filed March 29. 1965 13 Sheets-Sheet 11 INVENTOR COLOR TY July ll, 1967 R. K. H. cal-:BEL

NARROW BAND LONG RANGE COLOR TELEVISION SYSTEM INCORPOFATING COLOR ANALYZER 13 Sheets-Sheet 12 Filed March 29, 1965 Graff July 11, 1967 R. K. H. Geez-:L

NARROW BAND LONG RANGE COLOR TELEVISION SYSTEM INCORPORATING COLOR ANALYZER 13 Sheets-Sheet 155 Filed March 29, 1965 INVENTOR A. KM 6F86! i0/ Y B 62. WQQQQ msg-lr United States Patent O 3,330,904 NARROW BAND LONG RANGE COLOR TELEVI- SION SYSTEM INCORPORATING COLOR ANA- LYZER vRadames K. H. Gebel, Dayton, Ohio, assigner to the United States of America as represented by the Secretary of the Air Force Filed Mar. 29, 1965, Ser. No. 443,722 4 Claims. (Cl. 178-5.2)

ABSTRACT F THE DISCLOSURE The invention described herein may be manufactured i and used Aby or for the United States Government for governmental purposes without the payment to me of any royalty thereon.

In the transmission of information over great distances, such as encountered in space exploration, a narrow bandwidth is desirable in order to preserve a good signal-tonoise ratio. Frequency modulation is also preferred to amplitude modulation in order to desensitize the receiver to noise and to amplitude modulation of the desired signal by possible tumbling of the spacecraft. At the same time color information about the planets such as Mars and Venus is very important since it assists in forming a judgement as to which areas of the planet have ice, sand, lichens or other vegetation, water, etc. It is the principal object of the invention to provide a color television system particularly adapted to space transmission from the standpoint of conservation of bandwidth and simplicity of the transmitter. A furtther object of the invention is to provide a color analyzer that will determine the chromaticity of a color, i.e. its position in the C.I.E. (Commission International de lEclairage) color triangle, and its brightness.

Briefly. the television system is accordance with the invention comprises at the transmitter the above mentioned color analyzer which determines the chromaticity and brightness of each elemental area of the viewed scene. These two factors are converted to corresponding frequencies which are transmitted to the receiver by a frequency modulated radio link. At the receiver the brightness and chromaticity signals are recovered and used to control the brightness and color of a 3color cathode ray picture tube. In addition to its use in a television system, the chromaticity portion of the color analyzer may be used to determine chromaticity in terms of hue and saturation or whiteness and to control, for example, an automatic paint mixer or analogous apparatus in accordance therewith.

A more detailed explanation of the various aspects of p ICC the invention will be given with reference to the accompanying drawings in which FIG. 1 is a block diagram of apparatus for determining the chromaticity of a color,

FIG. 1A is a variation of FIG. 1 for simulating the subjective color sensations of the eye,

FIG. 2 shows details of the photoelectric system of FIG. l,

FIG. 3 is a schematic diagram of a ratio computer for use in FIG. 1,

FIGS. 4 and 4a show and explain the C.I.E. color plane,

FIG. 5 shows the tristimulus curves for the eye,

FIGS. 6, 7 and 8 show filter-photocathode combinations for approximating the tristimulus curves of the eye,

FIG. 9 shows another method for matching the tristimulus curves of the eye,

FIGS. l0, l1 and l2 show modifications of FIG. 1 for determining chromaticity in terms of hue and whiteness,

FIG. I3 shows a method of insuring that the electron beam falls on only one electrode in FIGS. 11, l2, 19 and 20,

FIG. 14 illustrates with FIGS. 1, 10, 11 and 12 an automatic paint mixer,

FIG. l5 is a block diagram of a color television transmitter in accordance with the invention,

FIG. 16 shows details of the color camera of FIG. 15,

FIG. 17 shows a flter-photocathode combination for producing the LRS function in the color television camera of FIG. 15,

FIG. 18 illustrates the method of deriving the intensity or brightness function in FIG. 15,

FIG. 19 shows one form of the color encoder of FIG. l5,

FIG. 20 shows another form of the color encoder of FIG. 15,

FIG. 21 is a block diagram of a color television re ceiver in accordance wit-h the invention,

FIGS. 22 and 23 show details of the color decoder of FIG. 21, and

FIG. 24 shows the I(7\) characteristic obtained from the filter-photocathode combinations of FIGS. 6, 7, 8 and 17.

It is known that the color of any luminous surface can be fully defined by three numbers X, Y and Z the values of which are Z=fE( .)Z(x)dx where E0) represents the spectral ldistribution of the light emanating from the surface and the functions OJ, Y0) and 20,), called the tristimulus values, represent the spectral sensitivities of three color sensors which, in accordanee with the Young-Helmholtz color theory, are in` each individual color sensitive area of the human retina. In tests conducted on a large number of observers the relative values of these functions for the spectrum of constant energy have been determined for the average observer and are shown in FIG. 5.

Changes in the amount of the radiation E0) received from the luminous surface,l i.e. changes in the brightness of the surface, change the absolute but not the relative values of X, Y and Z. Therefore, brightness is a factor in defining color and, in fact, the color sensation proiced by light of constant spectral content changes with e radiation intensity or brightness. What does not change ith brightness is termned the chromaticity of the color. hromaticity may be defined by three numbers x, y and z is clear that only two of the above three numbers are :quired to define a chromaticity, the numbers x and y eing normally used. If the values f x and y are plotted 'ith respect to x and y rectangular axes, then, it is aparent that all chromaticities lie within a triangle bounded y the lines x=0, y=0 and x-l-y=1. All chromaticities 'ithin this triangle, however, are not realizable, The real- :able chromaticities lie within an area in the triangle ounded by the locus of the chromaticities of all the monohromatie relations in the visible spectrum and a straight ne joining the extremities of this locus. The standard 2.I.E. color plane derived in the above manner is shown a FIG. 4. The line 1, extending from the point repreenting the chromaticity of the radiation of wavelength 80 mp at the extreme violet end of the spectrum to the oint representing the chromaticity of the radiation of Javelength 780 ma at the extreme red end of the spectrum, s the locus of the chromaticities of the visible mono- :hromatie radiations or spectral colors. The straight line L joining the extremes of this locus and completing the ioundary of the area of realizable chromaticities is the oeus of the chromaticities of mixtures 0f extreme spectral 'iolet and extreme spectral red which constitute the urple colors. The chromaticity for white is at the point t=0.33, y=0.33. When lights of two different chromaicities are additively mixed the resulting point in the :olor plane lies on a straight line joining the two chronatitices. Thus, as better seen in FIG. 4a, a mixture 0f t and B lies at a point such as C on the line joining A md B. the position of C being at the center of gravity of and B which are assigned weights equal to X-l-Y-l-Z. 'f now a color at point D is added to the color at C, the :hromaticity moves toward D along a straight line to a toint such as E a distance depending upon the amount of 3 added. Further, if a spectral color such as that at point is mixed with increasing amounts of W (white) the :hromaticity moves along a straight line toward W, the esulting mixture decreasing in saturation or increasing in whiteness as W is approached. Thus, in FIG. 4, lines 3 are ermed lines of constant hue or colorimetric purity and ines 4 are termed lines of constant saturation or whiteiess. It follows that any chromaticity can be specified in erms of hue and saturation (or degree of whiteness) yvhere hue is a color whose chromaticity lies on the specral line 1 or the purple line 2. Additive mixtures of my three colors having chromaticties G, H and I (FIG. la) can produce any color having chromaticity lying `vithin the area of the triangle defined by these three mints. Because of the curvature in two Sides of the area he realizable chromaticities, as shown in FIGS. 4 md 4a, there are no three realizable colors that can proiuce all of the visible colors; however, by a judicious :hoice of thc three primary colors, a high proportion of he visible colors may be produced by their mixture..

lt follows from the foregoing that the color sensation reduced in the brain when viewing a luminous surface s determined by the intensity of the light emanating from he surface, i.e. itsy brightness, and by its chromaticity which, except for the chromaticities lying on the spectral line and the purple line in the color plane, is not spectrally unique. More detailed information on the problem of color and color perception may be found in an article entiited The Colour Triangle by W. deGroot and A. A. Kruithof, appearing in the Philips Technical Review, Vol. 12, No. 5, November 1950, and in the book entitled The Threshold of Visual Sensation in Comparison with that of Photosensors, Its Quantum Aspect, Problems of Color Perception, and Related Subjects by R. K. H. Gebel available from the Superintendent of Documents, U.S. Government Printing Ofiice.

The color analyzer shown in FIG. l operates to determine the chromaticity of any given color and to position the beam of cathode ray tube 5 so that the spot of light on the screen occupies a position corresponding to the position of the chromaticity of the color in the color triangle. For direct reading of the chromaticity a transparent overlay of the color triangle of FIG. 4 may be provided on the screen of the cathode ray tube. As shown in FIG. 1, the analyzer is used to determine the chromaticity of the light reflected from a colored surface 6 which is illuminated by light from sources 7 and 8. The spectral distribution of sources 7 and 8 should correspond to that of the illumination under which the color of interest is to be normally observed. Light reflected from surface 6 enters photoelectric system 9 which has three sensors the outputs of which are designated X, Y and Z. The sensitivities of these sensors should correspond as nearly as possible to the functions XO) YO) and 7AM shown in FIG. 5. The outputs X, Y and Z are applied to adder 10 which has an output M=X}-Y-|-Z. The outputs X and M are applied to ratio computer 11 which has an output The outputs x' and y' are the rectangualr coordinates of the chromaticity and are applied to the horizontal and vertical deection circuits, respectively, of cathode ray tube 5. If the screen of tube 5 is provided with an overlay in the form of FIG. 4, as previously stated, the spot 0f light produced by the beam will indicate the position of the chromaticity in the C.I.F color triangle, from which the chromaticity may be read in terms of x', y' values or in terms of hue and saturation.

The apparatus of FIG. 1 constitutes an opte-electrical analogy of the human visual organs in determining chromaticity. As is known, if white light is pulsed at a frequency below the fusion frequency of the eye a sensation of color is produced. This is known as the Provost-Fechner-Benham subjective color phenomena. It has been assumed that these phenomena are due to transients in the outputs of the three color sensors in the retina. This effect may be simulated in the apparatus ofl FIG. l by inserting in the X, Y and Z outputs networks 13, 14 and 15 having different time constants. With this arrangement, the X, Y and Z outputs will have different values for pulsed white light than for steady white light with the result that the x', y' chromaticity values change and the chromaticity is displaced from the white point in the color triangle.

The details of the photoelcctric system 9 of FIG. 1 are shown in FIG. 2. The incoming light is split into three components, by a suitable arrangement of partially refleeting and totally reflecting mirrors and directed into the X, Y and Z sensors. The X, Y and Z sensors comprise photomultipliers preceded in cach case by a filter I, II or III and a neutral density filter 16, 17 or 18. For determinations relative to the CLE. color plane, the X, Y and Z sensors should have relative sensitivities corresponding to the X0), 'tx) and the Zta) functions, respectively, of FIG. 5, i.e. to the tristimulus values of the eye. These sensitivities are controlled by the transmission characteristics of filters l, II and III and the spectral responses of the photocathodes of the photomultipliers. FIGS. 6, 7 and 8 give filter-photocathode combinations approximating the desired functions. For FIG. 6 where two different filters and two different photocathodes are required a composite filter and a composite photocathode may be sponse of the photosensor 21, any desired overall characteristic may be obtained.

The ratio computers 11 and 12 in FIG. 1 may be any suitable device for producing a voltage proportional to the ratios indicated. An example is shown in FIG. 3. Referringy to this figure, the voltage M is converted by interrupter 21 and capacitor 22 into an alternating voltage clM of frequency f1 which is applied along with alternating voltage e of frequency f2. derived from source 23, to the control grid of tube 24 the amplifieationfactor of which may be controlled by varying the direct voltage E on its third grid. The direct voltage X is applied to a potential divider 25-26 producing a voltage kZX across resistor 26. The output of tube 24 at frequency f1 is cou pled to rectifier 27 through transformer 28 tuned to f1. The output of this rectifier, developed across resistor 29, has the value kaAlklM, where A1 is the gain of the tube 24 stage at l1. The difference between the voltages across resistors 26 and 29 is amplified by amplifier 30 having gain A3 to produce the gain control voltage E. The output of tube 24 at frequency f2 is coupled by transformer 31, tuned to f2, to recliner 32 which produces the output voltage x at potentiometer resistor 33.

The principle of operation of the circuit of FIG. 3 is to make the gain of stage 24 proportional to X/M and, since e is constant, x will then be a constant times the gain or a constant times X /M. This may be seen from the following equations:

If A3 is made very high, the term E/Aa approaches zero, since E is relatively small, and the expression for A1 becomes 3) 4 MX. l 1 kgkIM Since the gain A2 of stage 24 at f2 is a constant times the gain A1 at f1 The voltage y' is obtained in a similar manner.

FIGS. l0, 1l and 12 illustrate a modification of the ehromaticity analyzer of FIG. 1 that indicates chromaticity in terms of hue and whiteness. For this purpose two cathode ray tubes 34 and 3S are required as shown in FIG. 10. Cathode ray tube 34 determines the hue of the analyzed color and for this purpose has on the inner surface of its screen an electrode structure such as shown in FIG. 1l. The electrodes in this structure consist of a plurality of electrically separate roughly triangularly shaped electrodes 36 extending in the color plane from the spectral line and the purple line toward the white point. Each of these electrodes corresponds to a hue and is connected to an external circuit and to ground through a resistor 37. Consequently, when the electron beam rests on any particular electrode the beam current owing in the resistor 37 produces a voltage thereacross which may be amplified in amplifier 38 and applied to control line 39, each control line representing a particular hue. The electrodes 36 may be metallic films formed on the inner surface of the cathode ray tube screen by any of the known processes for accomplishing this.

Cathode ray tube 35 determines the whiteness of the i current owing through the corresponding load resistor 41 produces a voltage thereacross which may be amplified inv an amplifier 42 and applied to a control line 43, each control line corresponding to a degree of whitness.

In order to prevent the electron beam from impinging on more than one electrode in FIGS. ll and 12, the technique illustrated in FIG. 13 may be used. The space between adjacent electrodes 36 or 40 is provided with two small parallel wires or other conductors 44 and 45. These conductors are coupled through amplifiers to small detiection coils 46 and 47 on the cathode ray tube. As the beam 48 spills over the edge of an electrode and touches the adjacent conductor current Hows in the detiecting coil. The alignment of the coil and the direction of the current ow are made such as to oppose any further movement of the beam toward the conductor. With sufficient amplifier gain, the beam is restrained to a position that barely touches the conductor, as illustrated. In this manner the beam is prevented from impinging on both electrodes by being defiected toward the electrode adjacent to the conductor drawing the greater beam current. Several systems of this type are required to protect all edges of the electrodes in FIGS. 11 and 12 because of their different directions.

FIG. 14 together with FIG. 1 as modified in FIGS. l0, 11 and 12 consititutc an automatic paint mixer capable of viewing a particular color under normal lighting conditions and mixing a paint. that will match the color. The apparatus in FIG. 14 comprises a stationary container 49 for white paint having an outlet through an electrically actuated variable rate dispenser 50 controlled by the whiteness control lines from FIG. l2. There is also a container 51 for each of the hues which, in the example shown, are ten in number. The hue containers may be mounted on a movable structure 52, Stich as a turret,

so that the proper hue may be brought into position near the white outlet. When in position, contacts 53 and 54 make connection to an electrically operated constant rate dispenser 55. The hue control lines from FIG. 1l actuate a hue indicator 56 which indicates the hue to be brought into position. These control lines also connect to a switch 57 which is actuated by movable structure 52 to energize interlock relay 58 when the proper hue is in position. With the interlock relay energized, depression of operate button 59 energizes the variable rate dispenser 50 and the constant rate dispenser 55 of the selected hue for s long as the button is depressed, the rate of dispsener 0, as determined by which of the whiteness control tues is energized, being such as to give the required chroviaticity.

FIG. l shows the transmitter of a color television ystem incorporating a color analyzer of the type shown n FIG. l. In the television s) stem, in addition to transnitting the chromaticity of each elemental area in the cene, it is also necessary to transmit a signal representing he brightness of euch elemental area. Previously, as hown for example in the above cited article by de Groot nd Kruithof, the Y0) function has been considered the uminosity or visibility function of the eye. However, videnee including experience in providing the compatible :rey scale signal in the color television signal has shown hat this function is more like the I( function shown long with the O), TG) and Ot) in FIG. 18. Furher, the function I(\) in this gure is obtained by comfining the relative luminosity function for scotopic (rod) ision RISO) with the functions tlt), T() and '/Ot) or photopic (cone) vision in accordance with the equaion ndicatiug the likely influence of the rods in determining he eycs overall luminosity function. The color camera it) is therefore provided with an additional sensor havng a sensitivity linearly' rclattd to LRSO) illustrated in IG. 18. The output of this sensor, adiustable in ampliudc by potentiometer 61. together with the X, Y, Z out- `tuts reduced by a factor 0.33 by the potential dividers hown, are applied to adder 62 to produce the intensity nr brightness signal I at its output. The brightness signal 'requency modulates brightness' oscillator 63. The encoder S4 is a device for converting the chromaticities represented y the voltages x and y' to different frequencies. There ore. for each elemental area of the scene viewed by the :olor camera 60, a frequency representing chromaticity md a frequency representing brightness are applied to nixer 65 where they are linearly combined and applied as nodulating signals to FM transmitter 67. The blanking uilscs from blanking generator 66 are also applied to he encoder 64 and, as will be seen later, cause the encoder o have a xed reference frequency output during the nlanlting intervals.

As stated earlier. the television system described heren is intended for long range narrow bandwidth operaion as would be desirable in a system for space exploraion. In transmitting a color picture of a planet, for eximple` the system in most cases would not be called upon o transmit rapid motion. Therefore the frame rate and he scanning rate as provided by sweep generator 68 may wc very low which reduces the bandwidth requirements. lXlso the above described frequencies representing chronaticity and brightness may be in the low audio frequency range which further reduces the bandwidth repiirements.

The color camera 60 of FIG. 15 is shown in more deail in FIG. 16. Light from the area viewed by the camera s split into four components by a system of partially ransparent and totally reflecting mirrors. Four television iickup tubes 69, 70, 71 and 72 are provided, each receivng one of the four light components through a pair of iltcrs the first of which, number I, II, III or IV, has a spectral transmission characteristic which, when taken .rith the spectral characteristic of the photocathode in he pickup tube, provides the desired spectral sensitivity for he particular channel. Neutral density filters 73, 74, 75 and 76 serve to adjust the relative output amplitudes if the four channels. As for the photoelectric system in FIG. l, FIGS. 6, 7 and 8 show filterphotocathode :ontbinations approximating the desired Ot), T0) and Zta) functions. In the case of FIG. 6, however, two

photocathodes and two filters are required. While this could bc accomplished in FIG. 2 by a composite filter and a composite photocathode, in FIG. 16 two filters and two pickup tubes would be required to match the curve in FIG. 6. However, there are two methods whereby a single tube may be used. One method is to provide a single filter-photocathode combination that closely approximates the tx) function of FIG. 6, which is possible in the present state of the art, and the other is to omit the 40G-500 ma portion of the function which can be done without a serious loss in color accuracy. FIG. 17 illustrates a filter-photocathode combination providing the function LRSOt) that approximates the LRSM) function. FIG. 24 illustrates the I function produced at the output of adder 62 with potentiometer 61 set so that K=0.3. This function closely approximates the I()\) funetion of FIG. 18 in shape. The amplitude may be adjusted by amplification if necessary.

The encoder 64 of FIG. 15 may take the form of a cathode ray tube 76, which is analogous to cathode ray tube 5 of FIG. l, having a resistive spiral 77 on the inner surface of its screen, as shown in FIG. 19. The spiral covers the area of the CIE. color plane containing the realizable chromaticitics, as seen in FIG. 4. When the beam impinges on the spiral, beam current flows through the spiral and resistor 78 producing a voltage Ec across this resistor the valuc of which depends upon the point in the spiral on which the beam falls. The spiral starts at the white point 79 in the CIE. plane and ends at thc point 80 representing the extreme violet end of the visible spectrum. Consequently, vt hen the x', y voltages represent the chromaticity of white the voltage Ec has a minimum value and when the x', y voltages represent the chromaticity of violet this voltage has its maximum value. At all other positions in the area Ec lies between these values, but has a zero value when the beam does not strike the spiral at all, which occurs during the` blanking intervals of the scanning process when the beam is cut ott by the blanking pulse applied to encoder 64 (FIG. 15). The voltage IEc controls the frequency of color oscillator 81 so that it oscillates at a different frequency for each resolvable chromaticity. The ability of the spiral to resolve elemental areas in the chromaticity diagram will of course depend for one thing upon the width of the resistive strips forming the spiral. The color oscillator 81 may be an oscillator of any type the frequency of which may be controlled by a direct voltage, for example, a multivibrator. The frenquency of the oscillator when Ec=0 may be transmitted as a reference frequency for the discriminators at the receiver, to be explained later. The technique of FIG. 13, although not shown in FIG. 19 for simplicity, may be used to prevent the beam from impinging simultaneously on adjacent turns of the spiral.

FIG. 2() shows another form which the color encoder may take. In this arrangement small elemental electrically separate conductive arcas 82 cover the chromaticity diagram rather than the spiral of FIG. 19. Each arca represents a resolvable chromaticity and is connected in series with resistor 78 through external resistors such as 83, 84 and 85, all having different values of resistance. Therefore, the value of Ec and the frequency of oscillator 81 depend upon which of the elemental arcas receives the electron beam. As the number of elemental areas is increased and their sizes become smaller the number of ehromaticities that may be resolved increases, the ultimate being a multiplicity of pin electrodes extending through the screen of the cathode ray tube. The technique of FIG. 13 may also be used in this case to insure that thc beam falls on only one elemental arca at a time.

The brightness oscillator 62 of FIG. l5 may be similar to color oscillator 81 since the output of adder 62 is a direct voltage; however, the frequency bands ofthe two oscillators should be selected so as not to interfere with each other. As for the color oscillator, the frequency of the brightness oscillator during the blanked intervals of the scanning process when the output of adder 62 is zero is taken as the reference frequency.

FIG. 21 shows the receiving end of the color television system. The FM signal from the transmitter of FIG. 15 is received and demodulated by FM receiver 86, the brightness, brightness reference, color and color reference frequencies appearing in the receiver output. These signals are directed into dilerent channels by brightness, brightness reference, color and color reference bandpass filters 87, 88, 89 and 90, respectively and after amplitude limitation are applied to discriininators 91, 92, 93 and 94 for conversion to proportionate direct voltages.

As stated earlier, the color reference frequency is transmitted during the blanking intervals. Therefore the output of the color reference discriminator 95 may be used as a blanking pulse andfor this purpose is added to the brightness signal in adder 96 and applied to the intensity control electrode in 3-color cathode ray reproducer 97 for controlling the intensities of the three beams simultaneously. This is shown schematically in FIG. 22. The output of discriminator 95 is also applied to synchronizing signal separator 98 which separates the horizontal and .vertical blanking pulses on the basis of their relative durations and applies them as synchronizing signals to horizontal and vertical sweep generators 99 and 100 which supply sweep voltages to reproducer 97. The color and brightness reference signals are indicated by frequency indicators 101 and 102, respectively, and this information is used in aligning color and brightness discriminators 94 and 92 to give the correct color and brightness outputs should frequency drift occur in the color and brightness oscillators at the transmitter. This alignment may be either automatic or manual, the latter being feasible in the described system because of the low rate at which information is transmitted.

The color signal obtained from discriminator 94 is applied to color decoder 103 which causes the three vbeams of the cathode ray tube reproducer 97 to be adjusted to the relative intensities required to reproduce the color called for by the magnitude ot the color signal. The color decoder is shown in FIGS. 22 and 23. It comprises a cathode ray tube S.having a single row of small phosphor areas 106 arranged in a straight line on its screen as seen in the enlarged cross section of the screen shown in FIG. 23. The color signal from color discriminator 94 and low pass filter 104 (FIG. 21), which is a direct voltage corresponding to the encoder 64 output in FIG. l5, is applied to a detiection system for tube 105 which detiects beam 107 in a single direction along the row of phosphor areas 106. The phosphor areas may have an electron pervious aluminum backing 108 for increased efficiency. Small conductors 44 and 45 may also be included between the phosphor areas to insure that the beam falls on only one phosphor area at a time in accordance with the technique of FIG. 13. On the outt,

side of the end plate of tube 105 directly opposite each of the phosphor areas is situated a photoconductor element 109 which receives light from the phosphor area when the phosphor area is energized by the beam. The photoconductors have one common lead 110 connected to ground and individual leads 111 coupled through load resistors 112 and a source of voltage (not shown) to ground to complete the circuit. The voltages developed across these load resistors are applied as control voltages to an equal number of like color control circuits for 3-color picture tube 97. Two of these circuits are shown in FIG. 22. Tube 113, which is the input tube for one of the control circuits, is connected as a cathode follower and has its output applied to the control grids of pentodes 114, 115 and 116 in parallel. When light is not being received by the photoconductor 109 associated with tube 113 this tube is biased to cutoff, or to sufficiently low conduction that the grid voltages for tubes 114, 115 and 116 are below the cutoff point. On the other hand, when light is being received by the photoconductor element its 10 conduction increases, which increases the grid potential of tube 113 and raises the grids of tubes 114, 115 and 116 above cutoff, causing anode conduction in these tubes. The amount of conduction in each tube and hence the anode voltage of the tube may be adjusted by controlling the screen grid potential through the agency of potentiometer 117, 118 or 119. The anode voltages control the biases and therefore the beam intensities of the blue, green and red guns in the color tube 97. In this manner, the anode voltages in each set of three tubes is adjusted to produce a color on the screen of tube 97 that has the chromatcity represented by the phosphor area in tube with which the control circuit is associated.

Where the frame frequency is too low for direct viewing of the received picture a color camera 120, as seen in FIG. 2l, may be used to photograph the image on the screen of tube 97 as it is formed. The vertical synchronizing signal may be used to advance the camera. Also, a tape recorder 121 may be used to record the complete incoming color signal which is easily done because of the low frequencies involved.

I claim:

1. A color television system comprising: a color television camera with associated horizontal and vertical sweep circuits and a horizontal and vertical blanking pulse generator, said camera having X, Y and Z output signals supplied by X, Y and Z television pickup tubes having sensitivities that are functions of wavelength substantially corresponding to the spectral distribution curves of the three coior sensors of the eye, and having an LRS output signal supplied by a television pickup tube having a sensitivity that is a function of wavelength substantially corresponding to the spectral distribution of the eyes sensitivtiy for scotopic vision; means for adding the X, Y and Z signals to produce a sum signal M; means receiving said sum signal and said X signal for producing an x' signal equal to the ratio X/M, and means receiving said sum signal and said Y signal for producing a y signal equal to the ratio Y/M, said x' and y' signals representing the rectangular coordinates of chromaticities; a color encoder receiving said x and y signals and producing an audio frequency color signal of ditierent frequency for cach chromaticity represented thereby, said encoder also receiving blanking pulses from' said blanking generator and producing a fixed frequency reference signal during each of said pulses; means adding said X, Y, Z and LRS signals in predetermined relative amounts to produce an intensity signal; means receiving said intensity signal and producing an audio frequency brightness signal the frequency of which is proportional to the magnitude of said brightness signal; a radio transmitter; means for applying said color signal and said brightness signal as modulating signals to said transmitter; a radio receiver for receiving and demodulating the signal radiated by said transmitter; bandpass filters coupled to the output of said receiver for separating the brightness signal, the color signal and the color reference signal from the receiver output; discriminators coupled to the outputs of said filters for producing signals having amplitudes directly related to the frequencies of the brightness, color and color reference signals, respectively; a cathode ray color image reproducer having three color electron beam guns; means adding the output of the brightness signal discriminator and the output of the color reference signal discriminator together and means for controlling alike the intensities of the beams in said three guns in accordance with the sum of these outputs, the output of said color reference signal discriminator acting as blanking pulses; horizontal and vertical sweep generators coupled to said image reproducer; means coupled to the output of said color reference signal discriminator for separating the horizontal and vertical blanking pulses and utilizing same to synchronize the horizontal and vertical sweep generators, respective- 1y; a plurality of normally inoperative color control cirrits coupled in parallel to the three color guns of said .tage reprodueer, cach control circuit being adjusted to roduce when operative a dillerent color in said reproucer; and a color decoder coupled to theoutput of the alor signal discriminator and to said color control ciraits for rendering one of said control circuits operative t a time depending upon the magnitude of said color sigal discriminator output.

2. Apparatus as claimed in claim 1 in which said en- Jder comprises a cathode ray tube and associated high oltage supply, said tube having a beam intensity control lectrode and two rectangularly related detlecting means; leans applying said :r' signal to one deliecting means and tid y signal to the other; means for applying said blanklg pulses to said beam intensity control grid; a resistive piral on the beam side of the screen of said cathode ray tbe covering an area corresponding' to the area of reazable chromaticities in the CLE. color plane; and ex- :rnal lead connecting one end of said spiral through a ad resistor to thc positive terminal of the high voltage Jnree for said tube whereby the voltage across said load :sistor depends upon the point in said spiral on which te beam of said tube impinges; a variable frequency osillator; and means for applying the voltage across said )ad resistor to said oscillator as a frequency control oltage.

3. Apparatus as claimed in claim 1 in which said enodcr comprises a cathode ray tube and associated high tillage supply, said tube having a beam intensity control lectrode a'id two rectangulnrly related deflccting means; icans applying said signal to one deeeting means and aid y' signal to the other; means for applying said blankng pulses to said beam intensity control grid; a plurality of elemental electrically separate conductive arcas on the beam side ofthe screen of said cathode ray tube covering an area corresponding to the arca of the realizable chromaticitics in the (lill. color plane; external leads connecting leach elemental conductive area through a different series resistor and a load resistor to the positive terminal of the high voltage source for said tube whereby the voltage across said load resistor depends upon the elemental area on which the beam of said tube impingcs; a variable frequency oscillator; and means for applying the voltage across said load resistor to said oscillator as a frequency control voltage.

4. Apparatus as claimed in claim 1 in which said decoder comprises a cathode ray tube having deecting means for detlecting its beam along a line on the tube screen; means for applying the output of said color signal discriminator to said dcecting means; and means arranged along said line of deflection and cooperating with said beam and connected to said color control circuits for rendering one of said control circuits operative at a time depending upon the position of said beam along said line of deflection.

References Cited UNITED STATES PATENTS JOHN W'. CALDVVJLL. Acting Primary Exrmrner.

J. A. OBRIEN, Assfxmlrl Examiner. 

1. A COLOR TELEVISION SYSTEM COMPRISING: A COLOR TELEVISION CAMERA WITH ASSOCIATED HORIZONTAL AND VERTICAL SWEEP CIRCUITS AND A HORIZONTAL AND VERTICAL BLANKING PULSE GENERATOR, SAID CAMERA HAVING X, Y AND Z OUTPUT SIGNALS SUPPLIED BY X, Y AND Z TELEVISION PICKUP TUBES HAVING SENSITIVITIES THAT ARE FUNCTIONS OF WAVELENGTH SUBSTANTIALLY CORRESPONDING TO THE SPECTRAL DISTRIBUTION CURVES OF THE THREE COLOR SENSORS OF THE EYE, AND HAVING AN LRS OUTPUT SIGNAL SUPPLIED BY A TELEVISION PICKUP TUBE HAVING A SENSITIVITY THAT IS A FUNCTION OF WAVELENGTH SUBSTANTIALLY CORRESPONDING TO THE SPECTRAL DISTRIBUTION OF THE EYE''S SENSITIVITY FOR SCOTOPIC VISION; MEANS FOR ADDING THE X, Y AND Z SIGNALS TO PRODUCE A SUM SIGNAL M; MEANS RECEIVING SAID SUM SIGNAL AND SAID X SIGNAL FOR PRODUCING AND X'' SIGNAL EQUAL TO THE RATIO X/M, AND MEANS RECEIVING SAID SUM SIGNAL AND SAID Y SIGNAL FOR PRODUCING A Y'' SIGNAL EQUAL TO THE RATIO Y/M, SAID X'' AND Y'' SIGNALS REPRESENTING THE RECTANGULAR COORDINATES OF CHROMATICITIES; A COLOR ENCODER RECEIVING SAID X'' AND Y'' SIGNALS AND PRODUCING AN AUDIO FREQUENCY COLOR SIGNAL OF DIFFERENT FREQUENCY FOR EACH CHROMATICITY REPRESENTED THEREBY, SAID ENCODER ALSO RECEIVING BLANKING PULSES FROM SAID BLANKING GENERATOR AND PRODUCING A FIXED FREQUENCY REFERENCE SIGNAL DURING EACH OF SAID PULSES; MEANS ADDING SAID X, Y, Z AND LRS SIGNALS IN PREDETERMINED RELATIVE AMOUNTS TO PRODUCE AN INTENSITY SIGNAL; MEANS RECEIVING SAID INTENSITY SIGNAL AND PRODUCING AN AUDIO FREQUENCY BRIGHTNESS SIGNAL THE FREQUENCY OF WHICH IS PROPORTIONAL TO THE MAGNITUDE OF SAID BRIGHTNESS SIGNAL; A RADIO TRANSMITTER; MEANS FOR APPLYING SAID COLOR SIGNAL AND SAID BRIGHTNESS SIGNAL AS MODULATING SIGNALS TO SAID TRANSMITTER; A RADIO RECEIVER FOR RECEIVING AND DEMODULATING THE SIGNAL RADIATED BY SAID TRANSMITTER; BANDPASS FILTERS COUPLED TO THE OUTPUT OF SAID RECEIVER FOR SEPARATING THE BRIGHTNESS SIGNAL, THE COLOR SIGNAL AND THE COLOR REFER- 